A major earthquake would destroy buildings, roads and bridges along hundreds of miles. The cascading collapse of power, communications and transportation systems would plunge Middle Tennessee into a disaster that would make the May flood seem minor.

Seismologists estimate a 25% to 40% probability of a major quake within the next 50 years in the New Madrid Seismic Zone, which stretches from Memphis to southern Illinois.

The threat is so great that Tennessee and seven other states have adopted catastrophe plans for an earthquake. State and federal emergency officials are meeting today in Nashville to figure out how to allocate scarce rescue resources if a New Madrid quake hits.

After Hurricane Katrina devastated New Orleans and emergency responses fell short, all states were ordered to identify the greatest catastrophe that could befall them.

"New Madrid is our biggest threat," said Jeremy Heidt of the Tennessee Emergency Management Agency. "The May flood is such a big event, but it's really minor compared to something like this."

In fact, the flood showed how great the threat is. Ground movement of a few inches from the rain collapsed Highway 7 in Maury County. The road is still closed, and state officials will replace it with a bridge.

"That is minor compared to what the quake would do," Heidt said. "Basically, the road won't be there. The bridge will have collapsed. The approach to the bridge will collapse."

Middle Tennessee residents would see chimneys collapsing and structural cracks in older buildings, but they would feel the loss of power most.

"We'd be plunged into darkness, some of us without feeling the quake," Heidt said, as downed power lines and collapsed stations shut down electricity to 2.6 million in the eight states.

"All communications would be out. All air travel would be out as the FAA air control would go down. All rail travel would fail. Ports would shut down; oil and natural gas pipelines could be off line."

Events are planned next year to raise the public's awareness and persuade people to plan and prepare, Heidt said.

One will be the first Great Central U.S. Shake-Out. At 10:15 a.m. April 28, people will be urged to imagine a 6.0 quake has hit somewhere within the New Madrid zone.

"Take a minute. Ask yourself: Where am I? Where is your family? How would you get home? Where would you gather?" Heidt said. "Then take it in small bites. Create a plan, put together a disaster kit, set up a communications plan."

Unaware of threat

Tennesseans will need to be self-sufficient for at least 72 hours for food, water and shelter. But most are unaware and unwilling to acknowledge an earthquake risk. "It's been 200 years. It doesn't enter into the daily consciousness," Heidt said.

Four earthquakes with magnitudes between 7.0 and 7.7 hit the New Madrid zone between December 1811 and February 1812. The earth dropped 20 feet to form Reelfoot Lake. Huge waves swamped boats on the Mississippi River. Chimneys and buildings crashed down in Memphis and St. Louis. Church bells rang 1,200 miles away in Boston. Those quakes were among the most powerful to strike the United States since records have been kept.

Tennessee actually faces more risk from an earthquake than does California, because the impact area is so much larger. For example, a 1976 quake in Arkansas that measured 5.0 was felt in five states, including in Nashville. A 5.0 quake in California "would be felt in a few counties," said Gary Patterson, director of education and outreach at the Center for Earthquake Research and Information at the University of Memphis.

That's because California quakes originate on faults and travel through rock and sand. The New Madrid occurs much deeper on plates, and the energy moves farther through the loose soil.

Gujaret, India, has geology similar to that of the New Madrid zone, Patterson said. A 7.7 quake there in 2001 killed more than 20,000 people and destroyed 600,000 buildings.

Katrina Prods States

Tennessee began preparing after Hurricane Katrina in 2005, when states were ordered to identify the worst potential catastrophe. A plan adopted in October 2008 details actions, from ordering portable toilets to flying planes over highways to map damage.

Crucial infrastructure in West Tennessee is being retrofitted to minimize damage. Electrical substations there have been braced so they don't collapse. The Memphis water plant has been strengthened so it can still treat drinking water even if broken water mains can't deliver. "At least we'll have a water source there rather than have to truck water in from hundreds of miles away," Heidt said.

The states' plans are being reviewed at this week's meeting to see where the gaps are and how to fill them with federal resources. "All eight states will need all the same resources," Heidt said. "What this meeting hopes to do is, if there is a quake, is not to reduce it to eight governors clamoring for attention … so it is not based on who asks first or who screams the loudest or who has the most political pull."